1. Field of the Invention
The present invention relates to a polishing pad and a method for producing the same. More specifically, it relates to a polishing pad which has a polishing layer comprising a polymer matrix and water-soluble particles dispersed in the polymer matrix, and a method for producing the same. The pad can be suitably used for polishing the surfaces of a semiconductor wafer and other objects to be polished.
2. Description of the Related Art
As a polishing method capable of forming a surface with a high degree of smoothness, CMP (Chemical Mechanical Polishing) has been receiving attention in recent years. In the CMP, a surface to be polished is polished by sliding a polishing pad and the surface against each other with slurry which is a water-based dispersion having abrasive particles dispersed therein caused to flow down on the surface of the polishing pad from above. One of factors which significantly affect productivity in this CMP is a polishing rate. It is conceived that this polishing rate can be significantly improved by increasing the amount of retained slurry from a conventional amount.
In the CMP, heretofore, a polyurethane foam containing fine air bubbles is used as the polishing pad, and polishing is performed with the slurry retained in holes (hereinafter referred to as “pores”) opened on a surface of the resin foam.
However, it is difficult to control the degree of foaming in the polyurethane foam to a desired degree. It is very difficult to control the sizes of the air bubbles, a foaming density and other properties uniformly throughout the foam. Consequently, the quality of the polishing pad comprising the polyurethane foam varies, thereby causing a variation in the polishing rate and the state of the produced polishing pad.
Various resins having soluble materials dispersed therein are known as polishing pads whose formation of pores by foaming can be controlled more easily (JP-A 8-500622 and JP-A 2000-33552, JP-A 2000-34416 and JP-A 2001-334455). Of these publications, the former two publications suggest the effectiveness of the polishing pad containing a soluble material. However, studies with respect to a polymer matrix when actually used as the polishing pad have not been made. Meanwhile, in the latter two publications, constitutional materials thereof are studied, and more stable polishing and an improvement in polishing rate are recognized. However, much more stable polishing and further improvements in slurry retainability and the polishing rate are required.
In addition, a further improvement in the level of flattening a substrate to be polished is also required.